A liquid crystal display has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the likes. The liquid crystal display generally includes a liquid crystal panel and a backlight module opposite to the liquid crystal panel. The liquid crystal panel includes a plurality of pixel units for displaying images.
Referring to FIG. 5, this is a circuit diagram of a pixel unit 5 of a typical liquid crystal display (not labeled). The pixel unit 5 includes a gate line 51, a data line 52, a thin film transistor 53, a pixel electrode 54, a common electrode 55 and a liquid crystal layer (not shown) sandwiched between the pixel electrode 54 and the common electrode 55. The thin film transistor 53 includes a gate electrode 531 coupled to the gate line 51, a source electrode 532 coupled to the data line 52, and a drain electrode 533 coupled to the pixel electrode 54. The pixel electrode 54, the common electrode 55 and the liquid crystal layer cooperatively form a liquid crystal capacitor 50.
Typically, the common electrode 55 is applied with a predetermined common voltage Vcom, and the pixel electrode 54 is applied with a gray-scale voltage Vd. The common voltage Vcom of the common electrode 55 and the gray-scale voltage Vd of the pixel electrode 54 generate an electric field. The strength of the electrical field controls an amount of light beams transmitting through the liquid crystal capacitor 50. Thus, the pixel unit 5 displays an image with a desire gray-scale level. Generally, the gray-scale voltage of the pixel electrode 54 is switched from a positive value to a negative value with respect to the common voltage Vcom of the common electrode 55, in order to avoid deterioration of the liquid crystal layer.
Referring to FIG. 6, a sequence waveform diagram of the gray-scale voltage and the common voltage is shown. When the pixel unit 5 is switched on, the gray-scale voltage Vd is generated earlier than the common voltage Vcom. When the gray-scale voltage Vd is applied to the pixel electrode 54, the common voltage Vcom is still rising and does not reach a predetermined value. Thus, a voltage difference between the common electrode 55 and the pixel electrode 54 varies during a preliminary period after the pixel unit 5 is switched on. Thus, the amount of transmission light beams varies during this period. Therefore, the viewer can feel flickering.
Furthermore, when the liquid crystal display is powered off, the pixel unit 5 is switched off, and the common voltage Vcom slowly drops to 0V. Thus, the voltage difference still exists between the common electrode 55 and the pixel electrode 54, and the electric field still exists for allowing the amount of transmission of light beams. Therefore, a residual image is induced.
What is needed, therefore, is a liquid crystal display which can overcome the above-described deficiencies. What is also needed, is a driving method of such liquid crystal display.